Gas for removing deposit and removal method using same

ABSTRACT

The invention relates to a gas for removing deposits by a gas-solid reaction. This gas includes a hypofluorite that is defined as being a compound having at least one OF group in the molecule. Various deposits can be removed by the gas, and the gas can easily be made unharmful on the global environment after the removal of the deposits, due to the use of a hypofluorite. The gas may be a cleaning gas for cleaning, for example, the inside of an apparatus for producing semiconductor devices. This cleaning gas comprises 1-100 volume % of the hypofluorite. Alternatively, the gas of the invention may be an etching gas for removing an unwanted portion of a film deposited on a substrate. The unwanted portion can be removed by this etching gas as precisely as originally designed, due to the use of a hypofluorite. The invention further relates to a method for removing a deposit by the gas. This method includes the step (a) bringing the gas into contact with the deposit, thereby to remove the deposit by a gas-solid reaction.

This application is a divisional of U.S. application Ser. No.10/705,532, filed Nov. 12, 2003, now U.S. Pat. No. 7,168,436 which is adivisional of U.S. application Ser. No. 09/208,022, filed Dec. 9, 1998,and now U.S. Pat. No. 6,673,262.

BACKGROUND OF THE INVENTION

The present invention relates to a gas, that is, a cleaning or etchinggas, for removing deposits by a gas-solid reaction and a removal methodusing the gas.

In thin-film device production process of semiconductor industry,optical device production process, super steel material productionprocess and the like, various thin films, thick films, powders, whiskersand the like are produced, for example, by chemical vapor deposition,(CVD), physical vapor deposition (PVD), sputtering, and sol-gel process.During the production of these materials, unnecessary deposits in theform of film, whisker or powder are inevitably formed, for example, on areactor's inner wall and a jig for supporting the object, as well as onthe object. This may cause the occurrence of unnecessary particles,making it difficult to produce films, powders, whiskers and the like ofgood quality. Thus, it becomes necessary to occasionally remove theunnecessary deposits, for example, by cleaning gas. Such a cleaning gasis required, for example, to have (1) a high reaction rate at which thecleaning gas reacts with unnecessary deposits to form volatilecompounds, (2) a relative easiness to make the exhaust gas of thecleaning unharmful, and (3) a relative unstableness in the atmosphere tomake the impact on the global warming smaller. Conventional examples ofthe cleaning gas are C₂F₆, CF₄, C₄F₈, NF₃ and ClF₃. These compounds,however, have the following defects. Firstly, ClF₃ is highly reactive,and thus may do damage to materials conventionally used for theapparatus, when ClF₃ is used at a high temperature or with theassistance of plasma. Secondly, NF₃ is low in reactivity unless thereaction temperature is at least 300° C., and thus may be impossible toremove unnecessary deposits accumulated in the piping of the apparatusand the outside of the plasma region. Furthermore, it is necessary tohave a high temperature in order to make the exhaust gas unharmful.Thus, the cost for conducting the cleaning becomes relatively high.Thirdly, each of C₂F₆, CF₄ and C₄F₈ has the following defects. That is,it may be impossible to remove unnecessary deposits accumulated in thepiping of the apparatus and the outside of the plasma region.Furthermore, a fluorocarbon(s) will accumulate by the plasma cleaning.If oxygen is added in order to decrease the amount of the accumulationof the fluorocarbon(s), an oxide(s) will accumulate instead. Since eachof C₂F₆, CF₄ and C₄F₈ is a very stable compound, it is difficult totreat the exhaust gas of the cleaning. In other words, these compounds(gases) will be stably present in the environment, and cause adverseimpact against the environment due to their high global warmingcoefficients or factors. Thus, it is necessary to have a hightemperature for the treatment of the exhaust gas. This makes the cost ofthe treatment relatively high.

An etching gas, which is analogous to the above-mentioned cleaning gas,is used for partially removing a thin film material in order to transferthe circuit pattern, for example, of LSI and TFT. Conventional examplesof this etching gas are CF₄, C₂F₆, CHF₃, SF₆, and NF₃. These gases havea problem of high global warming coefficient. Furthermore, these gasesare relatively stable gases. Thus, it is necessary to use a large amountof energy for generating, for example, CF₃ radicals and F radicals,which are useful as etchant. That is, the electric power consumptionbecomes large. Furthermore, it is relatively difficult to treat theunreacted etching gases, prior to the discharge into the atmosphere.Therefore, there is an urgent demand for an alternative etching gas(es)that can easily be made unharmful on the global environment and iscapable of achieving high precision etching.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a gas forremoving deposits, which gas can easily be made unharmful on the globalenvironment after the removal of deposits.

It is a more specific object of the present invention to provide acleaning gas for efficiently removing unnecessary deposits accumulated,for example, in an apparatus for producing semiconductor devices, whichcleaning gas can easily be made unharmful on the global environmentafter the removal of the deposits.

It is another specific object of the present invention to provide anetching gas for removing, as precisely as originally designed, anunwanted portion of a film deposited on a substrate, for example, forproducing thin film devices (e.g., LSI and TFT), which etching gas caneasily be made unharmful on the global environment after the removal ofthe unwanted portion.

It is a still another object of the present invention to provide amethod for removing a deposit by the gas.

According to the present invention, there is provided a gas for removingdeposits by a gas-solid reaction. This gas comprises a hypofluorite thatis defined as being a compound having at least one OF group in themolecule. We unexpectedly found that various deposits can be removed bythe gas and that the gas can easily be made unharmful on the globalenvironment after the removal of the deposits. The gas may be a cleaninggas for substantially completely removing the deposits. In other words,this cleaning gas is used for cleaning, for example, the inside of anapparatus for producing semiconductor devices. This cleaning gascomprises 1-100 volume % of the hypofluorite. We unexpectedly found thatvarious unnecessary deposits can efficiently be removed by the cleaninggas. Furthermore, either of plasma-assisted and plasma-less cleanings ismade possible by the cleaning gas. Alternatively, the gas according tothe present invention may be an etching gas for removing an unwantedportion of a film deposited on a substrate. In other words, the etchinggas is used, for example, in pattern transfer operations in theproduction of semiconductor circuits. We unexpectedly found that theunwanted portion can be removed by the etching gas as precisely asoriginally designed.

According to the present invention, there is provided a method forremoving a deposit by the gas. This method comprises the step (a)bringing the gas into contact with the deposit, thereby to remove thedeposit by a gas-solid reaction. The above-mentioned unexpected findingsare also obtained by this method.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view showing a multilayer structure used in theafter-mentioned Examples 1-3 and Comparative Example 1, which is priorto an etching of a SiO₂ insulator film with an etching gas; and

FIG. 2 is a view similar to FIG. 1, but showing the multilayer structureafter the etching.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A hypofluorite according to the present invention dissociates moreeasily than, for example, each of CF₄, C₂F₆, C₄F₈, and NF₃, and is lowerthan ClF₃ in reactivity. For example, O—F bond of a hypofluorite, thatis, trifluoromethyl-hypofluorite (CF₃O—F), has a bond dissociationenergy of 43.5 kcal/mol. This value is lower than that (61 kcal/mol) ofN—F bond of NF₃ and higher than that (37 kcal/mol) of Cl—F of ClF₃. Inother words, CF₃O—F releases active fluorine more easily than NF₃ and ismore stable than ClF₃. Although CF₃O—F does not have a high fluorinationstrength as that of F₂ or ClF₃, it is sufficient to make it possible toconduct a plasma-less cleaning. Furthermore, it is possible to removedeposits (contaminants) accumulated in the outside of the plasma regionby using an etching gas comprising a hypofluorite (e.g., CF₃O—F),although it has been impossible by using conventional plasma cleaninggases (e.g., CF₄). It should be noted that the hypofluorite is muchsmaller than ClF₃ in corrosiveness. That is, the hypofluorite doesrelatively little damage to general materials used for, for example, aninner wall of the apparatus. The hypofluorite is decomposed in the air,and thus has little to do with the global warming. Furthermore, thecleaning gas or etching gas according to the invention discharged fromthe apparatus can easily be decomposed by water or an alkali aqueoussolution, for example, of alkali scrubber. Thus, the cleaning gas oretching gas itself is not discharged into the environment, nor producesglobal warming gases (e.g., C₂F₆ and CF₄). Therefore, the cleaning gasor etching gas according to the present invention does not causesubstantial environmental problems. The etching gas according to theinvention is capable of having a higher etching rate and a higher aspectratio than those of, for example, CF₄.

In the invention, examples of the deposit, which can be removed bycleaning with the cleaning gas or by etching with the etching gas, areB, P, W, Si, Ti, V, Nb, Ta, Se, Te, Mo, Re, Os, Ru, Ir, Sb, Ge, Au, Ag,As and Cr, and oxides, nitrides, carbides and alloys of these elements.The deposit, which is partially removed by etching with the etching gas,may be formed on a substrate, such as silicon wafer, metal plate, glassplate, single crystal plate, or polycrystalline plate.

In the invention, the hypofluorite optionally has at least one selectedfrom halogen atoms, ether groups, alcohol groups, carbonyl groups,carboxyl groups, ester groups, amine groups, and amide groups. Ingeneral, hypofluorites have very great fluorination strengths.Therefore, it may not be preferable in the invention to use ahypofluorite that has a reducing group or a bond that is unstable interms of energy level. Preferable examples of the hypofluorite of theinvention are CF₃OF, CF₂(OF)₂, CF₃CF₂OF, CH₃COOF, (CF₃)₃COF, CF₂HCF₂OF,(CF₃CF₂)(CF₃)₂COF, CH₃OF, CFH₂OF, CF₂HOF, CF₃CF₂CF₂OF, and (CF₃)₂CFOF.The hypofluorite of the invention may be derived from a halogenatedhydrocarbon group, ether, alcohol, carboxylic acid, ester, amine oramide. In the invention, it is optional to use a hypofluorite that hasat least two OF groups in the molecule, because this hypofluorite has areactivity analogous to another hypofluorite having only one OF group inthe molecule.

In the invention, it is optional to use a hypofluorite itself as acleaning gas. That is, this cleaning gas contains 100% of thehypofluorite. This cleaning gas is capable of completely cleaningdeposits, which have been deposited on the inside of a chamber and itsexhaust pipes. These deposits may be CVD by-products or unnecessarydeposits made of materials that are the same as the materials of filmsformed on, for example, silicon wafer and glass substrates. Furthermore,the cleaning gas of the invention can be used for cleaning amulti-chamber type CVD apparatus, various batch-type CVD apparatuses, aCVD apparatus for epitaxial growth, and the like. The manner of excitingthe cleaning gas is not particularly limited. For example, highfrequency or microwave may be used for the excitation, depending on thetype of the apparatus. It is optional to excite the cleaning gas in theinside of the reaction chamber. Alternatively, it is optional to take aremote plasma method in which the cleaning gas is excited in the outsideof the reaction chamber, and then radical or ion is introduced into thereaction chamber.

In the invention, it is optional to prepare a cleaning gas by mixing ahypofluorite with an inert gas (e.g., He, N₂ and Ar) and/or at least onegas component selected from oxygen and oxygen-containing gases (e.g.,CO₂, CO, NO, NO₂, and N₂O). In fact, if deposits containing no oxygenare repeatedly removed, a very small amount of an organic fluoridehaving a white color accumulates on a low temperature portion of theexhaust pipe(s) of the apparatus. This organic fluoride is assumed to bea polymer made from ions and radicals, such as CF₃O⁺, CF₃ ⁺ and CF₂ ⁺,derived from the hypofluorite. We unexpectedly found that the formationof this organic fluoride is prevented by mixing a hypofluorite with theabove-mentioned at least one gas component. Although CO₂ and CO of theat least one gas component each contain carbon, which is an elementcausing the formation of the organic fluoride, these compounds eachcontain oxygen in the molecules, too. Therefore, it becomes possible tomake F-radicals long in lifetime. This may prevent the formation of thepolymer. In particular, it is preferable that the at least one gascomponent is in an amount from 0.4 to 90 volume %, based on the totalvolume of the at least one gas component and the hypofluorite. If it isless than 0.4 volume %, carbon may remain on the wall of the reactor orthe piping after the cleaning. If it is greater than 90 volume %, theoxidation of the surface of the deposit may occur predominantly. Thismay lower the cleaning rate too much.

In the invention, as mentioned above, the cleaning gas may be ahypofluorite itself or a mixture of a hypofluorite and the at least onegas component selected from oxygen and oxygen-containing gases.Furthermore, the cleaning gas may be diluted with an inert gas (e.g.,nitrogen, argon and helium). A suitable cleaning gas is chosen,depending on the type and thickness of the deposit to be removed, thetype of the material of the apparatus, and the like. In case that thecleaning gas is diluted, the hypofluorite concentration of the dilutedcleaning gas is preferably at least 1 volume %, more preferably at least5 volume %, still more preferably at least 10 volume %. If it is lessthan 1 volume %, the reaction rate may become too low.

In the invention, the cleaning conditions are not particularly limited.The temperature of the cleaning is preferably from 10 to 700° C., morepreferably from 20 to 600° C. If it is higher than 700° C., the reactormay corrode too much. If it is lower than 10° C., the reaction rate ofthe cleaning may become too low. The pressure of the cleaning is notparticularly limited. In fact, it is preferably from 0.1 to 760 Torr inplasma-less cleaning and preferably from 1 m Torr to 10 Torr inplasma-assisted cleaning

In the invention, the etching manner and the reaction conditions of theetching, in which the etching gas of the invention is used, are notparticularly limited. For example, the etching may be reactive ionetching (RIE) or electron cyclotron resonance (ECR) plasma-assistedetching. Due to the use of a hypofluorite for the etching gas, fluorineradicals reach the surface of a SiO₂ insulator film 2 that is to bepartially removed by the etching gas (see FIG. 1). Furthermore, CFn ionsimpinge on the surface of the film 2. With this, the film 2 is etchedaway in a vertical direction, thereby to form, for example, a contacthole in the film 2, as shown in FIG. 2. The side walls of the contacthole are protected by the accumulation of a fluorocarbon polymer,thereby to achieve an anisotropic etching. In particular, a large amountof CF₃+ ions are produced, as well as fluorine radicals, in plasma bythe hypofluorite. Therefore, the etching gas of the invention issuperior in etching efficiency. Furthermore, the etching gas of theinvention contains oxygen of the hypofluorite. With this, a fluorocarbonfilm accumulated on the side walls of the contact hole can efficientlybe removed, thereby to conduct an anisotropic etching.

In the invention, the etching can be conducted under various dry etchingconditions, for example, of plasma etching, reactive plasma etching, andmicrowave etching. The etching gas of the invention may be prepared bymixing a hypofluorite with an inert gas (e.g., He, N₂ and Ar) and/or atleast one other gas selected from, for example, HI, HBr, HCl, CO, NO,O₂, CH₄, NH₃, H₂, C₂H₂, and C₂H₆. In fact, it is preferable to add, tothe hypofluorite, at least one first gas component selected fromhydrogen and hydrogen-containing gases (e.g., CH₄, NH₃, HI, HBr, C₂H₂,and HCl), in the preparation of the etching gas, for the purposes of (1)reducing the amount of fluorine radicals, which accelerate isotropicetching, and (2) increasing the reaction selectivity toward SiO₂ overSi. Furthermore, the flow rate ratio of the at least one first gascomponent to the hypofluorite is preferably not greater than 10:1. Ifthis ratio is greater than 10:1, the amount of fluorine radicals, whichare useful for the etching, may become too low. It is preferable to add,to the hypofluorite, at least one second gas component selected fromoxygen and oxygen-containing gases (e.g., CO, NO, N₂O, and NO₂), in thepreparation of the etching gas, for the purpose of increasing theetching rate of metals over oxides and nitrides. It is particularlypreferable that the flow rate ratio of the at least one second gascomponent to the hypofluorite is not greater than 4:1. If this ratio isgreater than 4:1, the amount of fluorine radicals, which are useful forthe etching, may become too low.

In the invention, the gas pressure of the etching is preferably nothigher than 5 Torr, in order to conduct anisotropic etching. If the gaspressure is lower than 0.001 Torr, the etching rate may become too slow.The flow rate of the etching gas may vary, depending on the reactorcapacity of the etching apparatus and the size of wafer, and ispreferably from 10 to 10,000 standard cubic centimeters per minute(SCCM). The etching is conducted at a temperature preferably not higherthan 400° C. If this temperature is greater than 400° C., the etchingmay proceed isotropically. This lowers the etching precision, and theresist may be etched away too much. If the etching gas comprises theabove-mentioned at least one first and/or second gas component, itbecomes possible, for example, to increase the etching rate selectivitytoward the silicon oxide film over the silicon film in the preparationof the contact hole.

The following nonlimitative Examples are illustrative of the presentinvention.

EXAMPLES 1-4

In each of these examples, a test piece was prepared at first bythermally oxidizing the surface of a silicon wafer and then by forming apolycrystalline silicon film having a thickness of 200 μm through athermal decomposition of SiH₄. This test piece was put on the lowerelectrode of a plasma CVD apparatus. Then, the test piece was subjectedto an etching for 30 seconds by applying a high frequency or RF (radiofrequency) power to the lower electrode and by feeding an etching gas,shown in Table 1, having a pressure of 0.5 Torr, a flow rate of 100 SCCMand a temperature of 20° C. In this etching, the frequency of the highfrequency power source was 13.56 MHz, the power applied to the lowerelectrode was 0.2 W/cm², and the distance between the lower and upperelectrodes was 10 mm. The result (etching rate) of the etching is shownin Table 1.

TABLE 1 Etching Gas Etching Rate (Å/min) Example 1 CF₃OF 8,105 Example 2CF₃CF₂OF 7,769 Example 3 (CF₃)₃COF 9,606 Example 4 CF₂(OF)₂ 20,832

EXAMPLES 5-44 & COMPARATIVE EXAMPLE 1

In these examples and comparative example, Examples 1-4 were repeatedexcept in that the etching gas types were changed as shown in Table 2,that the etching gas pressure was 10 Torr in place of 0.5 Torr, that thegas temperature was changed as shown in Table 2, and that theapplication of a high frequency power was omitted. The results (etchingrates) are shown in Table 2.

TABLE 2 Temp. (° C.) Etching Gas Etching Rate (Å/min) Example 5 20 CF₃OF1,040 Example 6 CF₂(OF)₂ 1,953 Example 7 CF₃CF_(2OF) 990 Example 8(CF₃)₃COF 960 Example 9 CF₂HCF₂OF 780 Example 10 (CF₃CF₂)(CF₃)₂COF 970Example 11 CF₃OF 480 Example 12 CFH₂OF 660 Example 13 CF₂HOF 770 Example14 CF₃CF₂CF₂OF 910 Example 15 (CF₃)₂CFOF 930 Example 16 100 CF₃OF 3,230Example 17 CF₂(OF)₂ 4,385 Example 18 CF₃CF₂OF 2,780 Example 19 200 CF₃OF9,810 Example 20 CF₂(OF)₂ 10,259 Example 21 CF₃CF₂OF 6,620 Example 22300 CF₃OF 20,500 Example 23 CF₂(OF)₂ 49,853 Example 24 CF₃CF₂OF 9,880Example 25 400 CF₃OF 32,900 Example 26 CF₂(OF)₂ 59,560 Example 27CF₃CF₂OF 14,700 Com. Ex. 1 CF₄ 0 Example 28 500 CF₃OF 53,600 Example 29CF₂(OF)₂ 71,265 Example 30 CF₃CF₂OF 23,000 Example 31 600 CF₃OF 78,800Example 32 CF₂(OF)₂ 98,654 Example 33 CF₃CF₂OF 37,100 Example 34 700CF₃OF 99,600 Example 35 CF₂(OF)₂ 115,893 Example 36 CF₃CF₂OF 45,200Example 37 (CF₃)₃COF 37,000 Example 38 CF₂HCF₂OF 31,000 Example 39(CF₃CF₂)(CF₃)₂COF 34,500 Example 40 CF₃OF 25,000 Example 41 CFH₂OF31,500 Example 42 CF₂HOF 33,000 Example 43 CF₃CF₂CF₂OF 36,000 Example 44(CF₃)₂CFOF 35,200

EXAMPLE 45

In this example, a plasma CVD was conducted by using tetraethylsilicate(TEOS) and oxygen as raw materials, in an apparatus for conducing theplasma CVD. With this, SiO₂ having a thickness of about 0.05 to about 20μm deposited on the wall of the apparatus. The inside of the apparatuswas cleaned at 20° C. for 20 min by feeding cleaning gases of CF₃OF,CF₂(OF)₂ and CF₃CF₂OF by turns and by applying a high frequency power tothe lower electrode of the apparatus. Each cleaning gas had a pressureof 1 Torr and a flow rate of 100 SCCM. In this etching, the frequency ofthe high frequency power source was 13.56 MHz, the power applied to thelower electrode was 0.2 W/cm², and the distance between the lower andupper electrodes was 50 mm. It was found by an observation of the insideof the apparatus that the SiO₂ was completely removed by the cleaningwith each cleaning gas.

EXAMPLE 46

A tungsten film was formed by a thermal CVD in a cold wall typeapparatus for conducting the CVD. Then, it was found that thetemperature in the vicinity of a heater disposed in the reactor was 500°C., that the temperature of a gas diffusion plate was 40° C., and thatthe temperature of the reactor wall was from 20 to 300° C. Furthermore,it was found that unnecessary tungsten films deposited in many positionsin the apparatus. The thickest tungsten film deposited therein had athickness of about 120 μm. It was further found that a tungsten oxidepowder deposited in the piping of the apparatus. After the formation ofthe tungsten film, a first cleaning was conducted by allowing a cleaninggas of CF₃OF to flow through the apparatus at a flow rate of 1 standardliter per minute (SLM) for 30 minutes. Then, it was found by anobservation of the inside of the apparatus that the tungsten film of theinside of the reactor and the tungsten oxide powder of the piping werecompletely removed by the first cleaning. Then, a tungsten film wasformed again in the same manner as above in the apparatus. After that, asecond cleaning was conducted in the same manner as that of the firstcleaning except in that CF₃OF was replaced with CF₃CF₂OF. Then, atungsten film was formed again in the same manner as above in theapparatus. After that, a third cleaning was conducted in the same manneras that of the first cleaning except in that CF₃OF was replaced withCF₃)₃COF. Similar to the above, it was found by an observation of theinside of the apparatus that the tungsten film of the inside of thereactor and the tungsten oxide powder of the piping were completelyremoved by the second and third cleanings.

EXAMPLE 47

At first, four test pieces were prepared by a thermal CVD byrespectively forming a tungsten (W) film, a WSi film, a TiC film and aTa₂O₅ film on four nickel substrates each having a length of 10 mm and awidth of 20 mm and a thickness of 2 mm. Each film had a thickness of 50μm. Then, these four test pieces were put on the lower electrode of aplasma CVD apparatus. Then, an etching was conducted for 10 min at 20°C. by allowing an etching gas of CF₃OF to flow through the apparatus andby applying a high frequency power to the lower electrode. This etchinggas had a pressure of 0.5 Torr and a flow rate of 100 SCCM. In thisetching, the frequency of the high frequency power source was 13.56 MHz,the power applied to the lower electrode was 0.2 W/cm², and the distancebetween the lower and upper electrodes was 50 mm. After the etching, thetest pieces were taken out of the CVD apparatus and then analyzed withan X-ray microanalyzer. With this, the peaks of W, Si, Ti and Ta werenot found.

EXAMPLE 48

In this example, Example 47 was repeated except in that a Mo film, a Refilm and an Nb film, each having a thickness of 50 μm, were respectivelyformed on three nickel substrates each having the same dimensions asthose of Example 47 and that the etching was conducted for 3 min. Thepeaks of Mo, Re and Nb were not found by an analysis with X-ray microanalyzer.

EXAMPLE 49

In this example, Example 47 was repeated except in that a TiN film and aTi film, each having a thickness of 5 μm, were respectively formed bysputtering on two nickel substrates each having the same dimensions asthose of Example 47. The peak of Ti was not found by an analysis withX-ray microanalyzer.

EXAMPLE 50

In this example, Example 47 was repeated except in that an Au film, anAg film and a Cr film, each having a thickness of 2 μm, wererespectively formed by vacuum deposition on three nickel substrates eachhaving the same dimensions as those of Example 47, that the etching gasflow rate was 10 SCCM, and that the power applied to the lower electrodewas 0.315 W/cm². The peaks of Au, Ag and Cr were not found by ananalysis with X-ray microanalyzer.

EXAMPLE 51

At first, a nickel vessel was charged with commercial phosphorus (whitephosphorus), Ta, As, Ge, Se and B powders, each being in an amount of 5mg. Then, the nickel vessel was put on the lower electrode of a plasmaCVD apparatus. Then, an etching was conducted for 10 min at 20° C. byallowing an etching gas of CF₃OF to flow through the apparatus and byapplying a high frequency power to the lower electrode. This etching gashad a pressure of 1 Torr and a flow rate of 10 SCCM. In this etching,the frequency of the high frequency power source was 13.56 MHz, thepower applied to the lower electrode was 0.315 W/cm², and the distancebetween the lower and upper electrodes was 50 mm. After the etching, itwas found by an observation of the vessel and the inside of theapparatus that all the powders were completely removed.

EXAMPLES 52-64

In each of these examples, a silicon film was formed by using SiH₄ as araw material in an apparatus. After that, there were found in theapparatus silicon and polysilane powders, which were deposited in areactor of the apparatus, and a polysilane powder, which was depositedin the piping of the apparatus. This piping is outside of the plasmaregion. Then, a plasma-assisted cleaning was conducted a certain timesas shown in Table 3 for 30 min per one time of the cleaning for thepurpose of removing these powders of the apparatus. In this cleaning, acleaning gas of CF₃OF was allowed to flow through the apparatus at aflow rate of 1 SLM under a pressure of 1 Torr. Furthermore, oxygen andnitrogen were selectively allowed to flow therethrough, as shown inTable 3. During the cleaning, the temperature of the inside of thepiping was 20° C., and that of the inside of the reactor was from 40 to400° C. After the cleaning, the inside of the apparatus was observed,and the result of this observation is shown in Table 3. In Table 3, ◯means that the powders were completely removed from the inside of thereactor and the piping, and the deposition of an organic fluoride didnot occur; Δ means that the powders were completely removed from theinside of the reactor and the piping, but the deposition of an organicfluoride in the form of powder or film was found at an end portion(particularly a low temperature portion) of the piping; and □ means thata silicon oxide formed by oxidation of the polysilane powder deposited.In each of Examples 52-64, at least the inside of the reactor wascleaned.

TABLE 3 O₂ The Number Observation Flow Rate N₂ Flow Rate of CleaningsResult after (SCCM) (SCCM) (time(s)) Cleaning Example 52 0 0 1 ◯ Example53 0 0 2 ◯ Example 54 0 0 3 Δ Example 55 1 0 3 Δ Example 56 3 0 3 ΔExample 57 4 0 3 ◯ Example 58 4 0 10 Δ Example 59 100 0 10 ◯ Example 60500 0 10 ◯ Example 61 50 50 10 ◯ Example 62 5,000 0 10 ◯ Example 638,000 0 10 ◯ Example 64 9,000 0 10 □

EXAMPLES 65-70

In each of these examples, a silicon film was formed in an apparatus byusing SiH₄ as a raw material. After that, there were found in theapparatus silicon and polysilane powders, which were deposited in areactor of the apparatus, and a polysilane powder, which was depositedin a piping of the apparatus. This piping was outside of the plasmaregion. Then, a plasma-assisted cleaning was repeatedly conducted for 30min per one time of the cleaning for the purpose of removing thesepowders of the apparatus. In this cleaning, a cleaning gas of CF₃OF wasallowed to flow through the apparatus at a flow rate of 1 SLM under apressure of 1 Torr. Furthermore, an oxygen-containing gas shown in Table4 was allowed to flow therethrough, together with CF₃OF. During thecleaning, the temperature of the inside of the piping was 20° C., andthat of the inside of the reactor was from 40 to 400° C. After thecleaning, the inside of the apparatus was observed, and the result ofthis observation is shown in Table 4. In Table 4, ◯ means the same asthat of Table 3 of Examples 52-64.

TABLE 4 Oxygen- Flow Rate of Oxygen- containing containing ObservationResult Compound Compound (SCCM) after Cleaning Example 65 CO₂ 20 ◯Example 66 CO 50 ◯ Example 67 NO 20 ◯ Example 68 NO 100 ◯ Example 69 NO₂5 ◯ Example 70 N₂O 10 ◯

EXAMPLE 71

A thermal CVD was conducted in an apparatus such that a tungsten filmhaving a thickness from 10 to 20 μm was deposited on the wall of areactor of this apparatus. Separately, a mechanism for exciting a gaswith microwave was attached with the reactor via a piping. Then, aremote plasma-assisted cleaning of the apparatus was conducted for 10min using microwave plasma. In this cleaning, a cleaning gas of CF₃OFwas allowed to flow at a flow rate of 1,000 SCCM under a pressure of 0.1Torr. The microwave output was 50 W (13.56 MHz), and the substratetemperature was 18° C. After the cleaning, it was found that the insideof the reactor was completely cleaned and that a powder (i.e., a mixtureof tungsten and tungsten oxide) deposited in the piping was completelyremoved.

EXAMPLE 72

In this example, Example 71 was repeated except in that CF₂(OF)₂ wasused as the cleaning gas. After the cleaning, it was found that theinside of the reactor was completely cleaned and that a powder (i.e., amixture of tungsten and tungsten oxide) deposited in the piping wascompletely removed.

EXAMPLES 73-75 & COMPARATIVE EXAMPLE 2

In each of these examples and comparative example, as shown in FIG. 1, amultilayer structure was prepared by forming a SiO₂ insulator film 2 anda resist mask 3 on a single crystal silicon wafer 1. Then, an openingwas formed in the resist mask, as illustrated in FIG. 1. After that, themultilayer structure shown in FIG. 1 was put into an etching apparatusequipped with a power source for supplying a high frequency power of13.56 MHz. Then, an etching of an exposed portion of the insulator film2 was conducted for the purpose of making a contact hole in theinsulator film 2, as shown in FIG. 2. In the etching, an etching gasshown in Table 5 was allowed to flow through the apparatus at a flowrate of 50 SCCM under a pressure of 0.02 Torr with a RF (radiofrequency) power density of 2.2 W/cm². After the etching, the etchingrate of this etching, the selectivity of the etching toward theinsulator film 2 over the resist 3, and the aspect ratio weredetermined, and their results are shown in Table 5. Furthermore, theloss of shoulder portions 4 of the resist 3 (see FIG. 2) was checked,and its result is also shown in Table 5.

TABLE 5 Etching Loss of Etching Rate Aspect Shoulder Gas (Å/min)Selectivity Ratio Portions Example CF₃OF 5,453 6 At least 7 No 73Example C₂F₅OF 4,026 7 At least 7 No 74 Example CF₂(OF)₂ 7,563 6 Atleast 6 No 75 Example CF₄ 608 4 5 Yes 76

EXAMPLE 76

In this example, Example 73 was repeated except in that an argon gaswith a flow rate of 200 SCCM was added to the etching gas (CF₃OF) ofExample 73 and that the flow rate of CF₃OF was 10 SCCM.

EXAMPLES 77-84

In each of these examples, Example 73 was repeated except in that ahydrogen-containing gas with a flow rate shown in Table 6 was added tothe etching gas (CF₃OF) of Example 73 and the flow rate of CF₃OF waschanged as shown in Table 6. In fact, the total flow rate of CF₃OF andthe hydrogen-containing gas was adjusted to 100 SCCM in Examples 77-84,as shown in Table 6. The results of the etching rates of the insulatorfilm 2, which is made of SiO₂, and the silicon wafer 1, which is made ofSi, are shown in Table 6. It is understood from Table 6 that the etchingrate of the silicon wafer 1 has decreased drastically with the increaseof the flow rate of the hydrogen-containing gas, and in contrast theetching rate of the SiO₂ insulator film was relatively stable even withthe increase of the flow rate of the hydrogen-containing gas. In otherwords, it is understood that the SiO₂ insulator film can selectively beetched away by adding a hydrogen-containing gas into the etching gas(i.e., hypofluorite), over the silicon wafer. Furthermore, similarresults of the etching rates were also obtained by respectively usingCH₄, HI, HCl and HBr as hydrogen-containing gases.

TABLE 6 Etching Rate Flow Rate of (Å/min) Flow Rate Hydrogen- Hydrogen-Insu- of CF₃OF containing containing lator Silicon (SCCM) Gas Gas (SCCM)Film Water Example 77 100 H₂ 0 5,560 40,856 Example 78 99.9 H₂ 0.1 5,56038,856 Example 79 99 H₂ 1 5,560 18,856 Example 80 90 H₂ 10 5,260 5,189Example 81 70 H₂ 30 5,240 889 Example 82 60 H₂ 40 5,060 11 Example 83 10H₂ 90 3,596 0.5 Example 84 60 C₂H₂ 40 5,010 9

EXAMPLE 85

In this example, a first etching was conducted by etching a tungstenfilm in the same way as that of Example 73. The etching rate of thefirst etching was 39,554 Å/min. A second etching was conducted in thesame way as that of the first etching except in that oxygen with a flowrate of 10 SCCM was added to the etching gas (CF₃OF). The etching rateof the second etching was 400,259 Å/min. A third etching was conductedin the same way as that of the first etching except in that the tungstenfilm was replaced with a SiO₂ film. The etching rate of the thirdetching was 5,453 Å/min. A fourth etching was conducted in the same wayas that of the third etching except in that oxygen with a flow rate of10 SCCM was added to the etching gas (CF₃OF). The etching rate of thefourth etching was 9,865 Å/min. It is understood from the etching ratesof the first to fourth etchings that the etching rate of a metal film(tungsten film) increases more greatly by adding oxygen to an etchinggas, than that of an oxide film (SiO₂) does.

The entire disclosure of each of Japanese Patent Application Nos.9-349536 filed on Dec. 18, 1997, 10-239338 filed on Aug. 26, 1998, and10-239339 filed on Aug. 26, 1998, including specification, claims,drawings and summary, is incorporated herein by reference in itsentirety.

1. A method for removing a portion of a film deposited on a substratefor producing thin film devices, said method comprising bringing anetching gas into contact with said portion of said film, therebyremoving said portion by a gas-solid reaction, wherein said etching gascomprises a hypofluorite and at least one first gas component selectedfrom the group consisting of hydrogen, CH₄, NH₃, HI, HBr, C₂H₂, and HCl,and a ratio by volume of said hypofluorite to said at least one firstgas component is at least 1:10, wherein said film is made of SiO₂, andsaid substrate is made of Si.
 2. A method according to claim 1, whereinsaid hypofluorite is a compound having at least one OF group in themolecule and optionally having at least one group selected from thegroup consisting of halogen atoms, ether groups, alcohol groups,carbonyl groups, carboxyl groups, ester groups, amine groups, and amidegroups.
 3. A method according to claim 1, wherein said etching gasfurther comprises an inert gas.
 4. A method according to claim 1,wherein said etching gas further comprises at least one second gascomponent selected from the group consisting of oxygen andoxygen-containing gases.
 5. A method according to claim 4, wherein saidoxygen-containing gases are selected from the group consisting of CO,NO, N₂O and NO2.
 6. A method according to claim 4, wherein a volumeratio of said hypofluorite to said at least one second as component isat least 1:4.
 7. A method according to claim 1, wherein said etching gashas a pressure from 0.001 Torr to 5 Torr.
 8. A method according to claim1, wherein said etching gas is at a temperature of not higher than 400°C.
 9. A method according to claim 1, wherein said etching gas has a flowrate of from 10 to 10,000 standard cubic centimeters per minute.
 10. Amethod according to claim 2, wherein said hypofluorite is selected fromthe group consisting of CF₃OF, CF₂(OF)₂, CF₃CF₂OF, CH₃COOF, (CF₃)₃COF,CF₂HCF₂OF, (CF₃CF₂)(CF₃)₂COF, CH₃OF, CFH₂OF, CF₂HOF, CF₃CF₂CF₂OF, and(CF₃)₂CFOF.
 11. A method according to claim 10, wherein saidhypofluorite is selected from the group consisting of CF₃OF, CF₂(OF)₂,CF₃CF₂OF, CH₃COOF, (CF₃)₃COF, CF₂HCF₂OF, (CF₃CF₂)(CF₃)₂COF, CH₃OF,CFH₂OF, CF₃CF₂CF₂OF, and (CF₃)₂CFOF.
 12. A method according to claim 11,wherein said hypofluorite is selected from the group consisting ofCF₃OF, CF₂(OF)₂, CF₃CF₂OF, (CF₃)₃COF, (CF₃CF₂)(CF₃)₂COF, CF₃CF₂CF₂OF,and (CF₃)₂CFOF.
 13. A method according to claim 1, wherein said at leastone first gas component is selected from the group consisting ofhydrogen, NH₃, HI, HBr, C₂H₂, and HCl.
 14. A method according to claim1, wherein said hypofluorite is selected from the group consisting ofCF₃OF, CF₂HOF, CFH₂OF, and CF₂(OF)₂.
 15. A method according to claim 1,wherein said hypofluorite is CF₃OF.
 16. A method according to claim 1,wherein said at least one first gas component is selected from the groupconsisting of hydrogen, CH₄, NH₃, and HCl.